The present invention relates to a video information system and a display apparatus such as a television receiver or a monitor to which a component signal can be input.
In recent years, various kinds of recording media are found in the market and the kinds of recording systems of video signals are also diversified corresponding to the kinds of the recording media. For example, a recording system with a component signal is one kind. In the system, a video signal is recorded in the form of a component signal, that is, a luminance signal and color-difference signals. An example of a component signal is shown in a product catalog of Leader Electronic Co., Leader Electronic Measuring Instrument No. 38 91/92, pp. 98 to 101. An example of a video recording apparatus with a component signal is shown in an optical disk catalog 91-3 of Matsushita Electronic Industry Co. (issued on 1 Mar., 1991).
In general, in a video recording apparatus, a component signal is chrominance-modulated to obtain a carrier chrominance signal and further it is composed with a luminance signal to form an NTSC signal, and it is supplied to a display apparatus. On the other hand, on the side of the display apparatus, the NTSC signal is separated and demodulated in a reversed process of the above to bring it back to a component signal, and the component signal is displayed as a video signal. In the above operation, surplus processing is included such as: a component signal chrominance modulation composition of a luminance signal and a chrominance signal, an NTSC signal separation into a luminance signal and a chrominance signal, and chrominance demodulation of a component signal, which processing deteriorates the quality of an image. In order to eliminate the surplus processing and prevent the deterioration of picture quality, there will be provided an output of a component signal in a video recording apparatus and an input for a component signal in a display apparatus.
When a video recording apparatus and a display apparatus are connected through a component signal and a display device (for example, a Braun tube or a liquid crystal panel) of the display apparatus is driven with the signal, there occurs a problem that color reproducibility is worse in comparison with that in the case of a composite signal connection. That is, in the case of a general commercial TV receiver or monitor, when an RF signal, an NTSC composite signal, separated signals(a luminance signal and a carrier chrominance signal), etc. are input to the receiver or monitor in the process of demodulation of a carrier chrominance signal into color-difference signals with a chrominance demodulator, different demodulation axes from the demodulation (modulation) axes of the NTSC broadcasting standard are used to obtain optimum color-difference signals suited to the luminance media having different chromaticities of three primary colors from those of the NTSC broadcasting standard. The display device is driven with the optimum color-difference signals, so that the deterioration of color reproducibility can be prevented.
An example of obtaining the optimum color-difference signals are shown in a Japanese Patent Application, Laid-open No. 9406/72 which relates to a method for making a skin color in an image to be displayed be insensitive to the deviation of a chrominance signal (an error caused by the distortion in the phase or amplitude on a transmission path), and it is also effective for the improvement in color reproducibility. Japanese Patent Application No. 350477/91 corresponding to the above-identified copending U.S. application Ser. No. 988,667, filed Dec. 10, 1992 discloses further improvement in color reproducibility.
In the aforementioned disclosures, it is recognized that the xy chromaticity values of phosphors of three primary colors (red, green and blue) of an existing display apparatus are different from those of the NTSC standard, and the color reproduction area of a display apparatus is narrower than that of the NTSC phosphors. Therefore, it is widely known that distortion occurs in the color reproducibility in a displayed image. In particular, the differences in xy chromaticity values of green and red phosphors are large, so that the distortion in color reproducibility in reproduced images occurs in the vicinity of yellow-green, and the colors in the vicinity of yellow-green, that is, skin color and green, are compressed by yellow-green and the color reproduction of these colors is deteriorated as shown in the chromaticity diagram of FIG. 1. The aforementioned disclosures describe methods for improving the color reproduction problem.
The method of correction for color reproduction will be explained with respect to FIGS. 1-3. FIG. 1 shows the distortion in color reproduction caused by the differences between the existing xy chromaticity values of phosphors of three primary colors (red, green and blue) of a display apparatus (without being given the color reproduction correction) and those of the NTSC phosphors. The white circular marks show reproduced colors of the NTSC phosphors and the solid black circular marks show reproduced colors of phosphors of the existing display apparatus. The tip of an arrow mark shows the position of a reproduced color being distorted and a double circle of black and white expresses that the reproduced color is not distorted. The distortion in color reproduction characteristics of a display apparatus occurs in the vicinity of the axis 7 of a yellow-green signal caused by the difference between the color reproduction area 1 formed with the NTSC phosphors and the color reproduction area 2 formed with the phosphors in the existing display apparatus, in particular, caused by the differences in xy chromaticity values of green and red phosphors. Thereby, color reproduction distortion appears in a state where green 3 and skin color 5 are compressed by yellow-green 4.
The above-mentioned color reproduction correction method described in the Japanese Patent, Laid-open No. 9406/72 is a method in which skin color 5 and red 6 which are positioned so as to be compressed in the vicinity of yellow-green axis 7 are made to approach red, and the signals in the vicinity of red and skin color are made to be reproduced in their original areas by widening the demodulation angle between the B-Y axis and the R-Y axis in a chrominance demodulation circuit and further by increasing the demodulation gain of R-Y axis. FIG. 2 shows the result of correction of skin color 5 and red 6. The effect of the correcting direction 8 in color reproduction makes it possible to correct skin color 5 and red 6. With respect to green 3, correction is not possible.
In accordance with a color reproduction correction method, exclusive axes for red and green are provided in place of an R-Y axis of a color demodulation circuit and these axes are selectively used corresponding to the hue of an input signal. Thereby, skin color 5 and red 6 which are compressed in the vicinity of yellow-green axis are made to approach red, and the signals in the vicinity of skin color and red are made to be reproduced in their original areas, and further, green 3 which is compressed in the vicinity of the axis 7 is made to approach green, and the signals in the vicinity of green are made to be reproduced in their original areas. FIG. 3 shows the result of correction of three colors, skin color 5, red 6 and green 3, and the effect of the correcting direction 8 in color reproduction corrects skin color 5 and red 6, and the effect of the correcting direction 9 in color reproduction corrects green 3 in a manner disclosed in copending U.S. application Serial No. 07/988,667. Therefore, by the latter method more kinds of colors can be corrected than those by the former method.
As described above, when a signal is input in the form of a carrier chrominance signal, the deterioration in color reproduction caused by the difference between the xy chromaticity values of three primary colors of luminescent media of a display device and those of the NTSC broadcasting standard can be improved by the interposition of the above-described correction circuit in the process of chrominance demodulation.
When color-difference signals formed according to the NTSC broadcasting standard are input to the display device and the display device is driven by the signals, chrominance demodulation is not needed and the above-mentioned correction circuit is not interpositioned. Therefore, the deterioration in color reproduction caused by the difference between the xy chromaticity values of the three primary colors of the luminescent media of the display device and the xy chromaticity value of the NTSC broadcasting standard comes out without being corrected.
Accordingly, in a case where a video recording apparatus and a display apparatus are connected so as to supply to the display apparatus a component signal, color reproducibility is deteriorated in comparison with the case where an RF signal, an NTSC composite signal, or separated signals (a luminance signal and a carrier chrominance signal) are input. Therefore, there has been a problem that different colors from the original colors are reproduced in a display device.